This invention relates to a wireless input system for a computer. More particularly, it relates to a wireless input system for a computer which comprises, in combination, a pen-type input device having a light emitting element for emitting a pulse of light and an input device body for receiving the pulse of light emitted from the pen-type input device and calculating the position abscissa of the pen-type input device on the basis of the received pulse. Although the input device having the light emitting device is herein referred to as "pen-type input device" in order to distinguish it from the input device body, the outer shape or outline of the pen-type input device may be of any type, and is not limited to the pen-like shape.
The above-mentioned wireless input system for a computer has an optical system unit disposed in the input device body for detecting the light emitted from a source of light in the pen-type input device. The optical system unit usually comprises an optical filter, a lens, a lens holder which has an opening functioning as an aperture, and a photodetector. Such optical system units are disclosed in the commonly owned U.S. Pat. No. 5,166,668 of Aoyagi.
FIG. 12 shows the disclosed optical system units. As shown in FIG. 12, the optical system units of the input device body 4 include lenses 20a and 21a, and photodetectors or light receiving elements 20b and 21b. Furthermore, optical filters and lens holders are omitted in FIG. 12. Other elements depicted include the light pen 5 and a holder receptacle 39.
Furthermore, with such a conventional construction, there is a problem that the cost of parts greatly increases since two optical system units are used. Furthermore, with the system for processing a signal of very weak light similar to that of the present invention, I/V amplifiers with great amplification are usually used. Consequently, the system is affected by electromagnetic noises from peripheral electronic devices, which would result in malfunctions.
In order to reduce electromagnetic noises, it is required to completely shield the optical system unit from the outside, which leads to greater size of the device and higher cost of parts, and it is therefore difficult to realize a wireless input system for a computer which merely requires a small space, has a high precision and is low in cost.